1. Field of the Invention
The invention relates to a hydrokinetic torque converter and a positive displacement transmission fluid pump for an automatic transmission in a vehicle powertrain.
2. Background Art
Automatic transmissions for automotive vehicles may include multiple ratio planetary gearing in a transmission housing that is secured to an internal combustion engine housing. The gearing defines torque flow paths from the engine to a driven shaft of the transmission. The driven shaft is connected drivably to vehicle traction wheels through a suitable driveline and a differential-and-axle assembly. Typically, a hydrokinetic torque converter is situated within the transmission housing at a location intermediate the engine and the multiple ratio gearing.
The hydrokinetic torque converter includes a bladed impeller connected drivably to a crankshaft of an internal combustion engine. The impeller includes an impeller housing that surrounds a bladed turbine and a bladed stator. The impeller, the turbine and the stator define a torus fluid flow circuit, whereby torus flow developed by the impeller is received by the turbine. Turbine blading changes a tangential fluid flow velocity vector for the torus fluid flow, thus developing turbine torque.
The stator is located between the torus fluid flow exit section of the turbine blades and the flow entrance section of the impeller. The geometry of the blading of the stator changes the tangential velocity vector of the torus flow such that turbine torque relative to the torque of the impeller is enhanced.
The impeller is rotatably supported on an impeller hub shaft journalled in a relatively stationary pump housing that forms a wall of the transmission housing separating the hydrokinetic torque converter from the planetary gearing. A positive displacement gear pump, typically of the internal/external gear rotor type, is situated within the pump housing. A drive gear of the gear rotor pump is splined or otherwise drivably connected to the hub of the impeller. Thus, the torque developed by the engine, which drives the impeller, is effective to drive also the gear rotor pump.
The gearing includes fluid pressure-operated clutches and brakes. In a typical automatic transmission, the clutches and brakes establish and disestablish multiple gear ratios in the transmission gearing. A transmission control valve body controls pressure distribution from the pump to the clutches and brakes, as well as to a transmission lubrication oil system.
Fluid pressure distributor passages for the transmission clutches and brakes and for the lubrication oil system are in communication with the pump housing, and ultimately with a pressure discharge port of the pump. The pump also has a pressure inlet port or suction port that communicates with a fluid supply reservoir, which forms a part of the transmission assembly.
A driving connection between the impeller hub and the driving gear of the gear rotor pump can be a key-and-slot connection, a splined connection, or a connection established by registering flats, typically two diametrically opposed flats formed on the impeller hub shaft. The driving gear of the gear rotor pump may be formed with flats on the inner diameter of a central opening in the driving gear, which register with the flats formed on the impeller hub shaft.
The impeller hub shaft is journalled in the pump housing. The housing, in turn, is fixed to the transmission housing and forms a bearing support wall.
During high volume manufacturing operations for an automotive transmission mechanism, the planetary gearing is assembled in a first assembly step within the transmission housing. The pump housing, in a separate assembly step, is secured to the transmission housing. These assembly steps occur prior to the assembly of the hydrokinetic torque converter between the engine and the transmission bearing support wall.
The torque converter itself is manufactured and assembled as a separate sub-assembly independently of the assembly of the planetary gearing and the gear rotor pump in the bearing support wall. It then is assembled during a final assembly operation within the transmission housing. This requires the impeller hub shaft to be inserted through a bearing opening formed in the bearing support wall. If the driving connection between the impeller hub and the gear rotor pump includes flats formed on the impeller hub and on the driving gear of the gear rotor pump, it is necessary to establish registry between the flats as the impeller hub shaft is advanced through the bearing support wall.
In a subsequent step in a final assembly operation, a flexible drive plate connected to the engine crankshaft is secured to a radially outward portion of the impeller housing. If the flats formed on the impeller hub shaft at the time of final assembly are not in registry with the internal flats formed on the driving gear of the gear rotor pump, a secure driving connection between the impeller and the pump will not be established.
When a transmission is shipped to a vehicle assembly plant, the torque converter is held in place by straps secured to the transmission housing. The straps are removed prior to assembly of the transmission to an engine. It is possible at that point for the impeller hub shaft to become detached from the drive gear of the gear rotor pump. This will cause the drive plate to be flexed when the transmission is assembled to an engine at a vehicle assembly plant, thereby creating an axial force on the impeller and the impeller hub.
In a typical high volume manufacturing operation at a transmission manufacturing plant, an automatic transmission will be assembled to an electric dynamometer and tested prior to delivery of the transmission to an automotive vehicle assembly plant. If testing were to occur on a transmission at the transmission manufacturing plant when the impeller hub shaft is not indexed properly with respect to the drive gear of the gear rotor pump, again a reliable driving connection between the impeller and the gear rotor pump will not be established because of the out-of-registry condition of the flats on the impeller hub and on the driving gear of the gear rotor pump.
Whenever an out-of-registry condition exists, the pump will not develop a pressure required for the clutch and brake elements of the transmission. This will cause malfunctioning of the automatic transmission controls and will result as well in a lack of lubrication oil pressure. This condition can result in a failure of the friction elements of the clutches and brakes, which results in an increased rejection rate and increased manufacturing costs.